If you want to paint the top of your snowboard. You should take off the topsheet and start from the bottom of the top layer. After you paint it. You then apply polyurethane to the paint to seal it in! Also engine enamel paints with the glitter awesomeness in them, such as in this picture. Would look AMAZING!

Oh also. If you aren't going to take the topsheet off you should use rubbing alcohol to clean the top off.